A method of manufacturing nickel cadmium batteries which is now in commercial use, is generally characterized by starting with metal plate material, which (after processing) will form the battery electrodes, cleaning the plates in a caustic (NaOH) solution, impregnating the plate material with nickel, both by sintering and then by immersing the sintered material in a heated solution of nickel nitride and sodium hydroxide; and then washing the impregnated plates with heated distilled water to remove excess material including nickel nitride, sodium hydroxide and sodium nitride.
Once the impregnated material has been washed, the used wash water obviously carries with it impurities which will make it unsuitable for human consumption, and therefore in order to comply with environmental regulations, the water must be treated before it is discharged. Since this treating is ancillary to battery production it is desirable to minimize the economic impact of this waste water processing. One method which is now in use for minimizing the economic impact of this requirement for waste water processing is disclosed in co-pending application Ser. No. 162,544, filed June 24, 1980, incorporated herein by reference, and assigned to the assignee of this application; briefly stated, in accordance with the referenced application multiple sources of a wash medium are provided with progressively increasing impurity concentrations. Washing is effected in a number of wash steps equal to the number of different sources employed; sequential washing steps employing a wash medium of progressively decreasing impurity concentration. While this technique has the advantage of significantly reducing the quantity of wash medium required for a given quantity of batteries, it does not eliminate entirely the necessity for processing of waste wash water, since even with the cascaded washing disclosed in the aforementioned application, there comes a point at which the impurity concentration of the wash media inhibits further effective washing.
The aforementioned process for manufacture of nickel cadmium batteries, includes, as stated above, a requirement for sodium hydroxide solution, used in the impregnation step. In particular, a need exists for a sodium hydroxide solution of about 25% by weight. Providing this solution is effected by mixing more concentrated sodium hydroxide (in one embodiment, 50%) with water; and since the impregnation step requires sodium hydroxide solutions at elevated temperatures, it may also be necessary to heat the solution.